Germany's defense minister has advised U.S. President-elect Donald Trump not to get too close to Russian President Vladimir Putin and to treat NATO as an alliance of like-minded nations, rather than as a business.

"What his advisers will hopefully tell him and what he needs to learn is that NATO isn't just a business. It's not a company," Ursula von der Leyen told ZDF television on November 10, adding that the military alliance is guided by "shared values" and common historical experiences.

During his election campaign, Trump threatened to abandon U.S. allies in Europe if they do not spend enough on defense.

Von der Leyen cautioned Trump against being drawn in by Putin, noting that NATO had stood by the United States after the September 11, 2001, attacks.

"Donald Trump has to say clearly on which side he is. Whether he's on the side of the law, peace, and democracy or whether he doesn't care about all that and instead he's looking for a best buddy," she said.

Trump has expressed admiration for Putin and said he would seek an improved relationship with Russia.